a) Field of the Invention
The present invention relates to a solid state image pickup device, and more particularly to the structure of a solid state image pickup device suitable for realizing high resolution and capable of reading pixel signals of one frame at the same time.
b) Description of the Related Art
Charge transfer type solid state image pickup devices or so-called charge coupled devices (CCD) have been developed, and they are used with cameras of televisions, video tape recorders and the like of NTSC standards. In NTSC standards, an image of one frame is divided into signals of two fields through interlace scanning, and signal charges of photosensors of the first or second field are read at the same time. In other words, two photosensors are generally provided with one transfer stage.
Non-interlace scanning is necessary, however, for electronic still cameras or televisions of new standards. In this case, one photosensor is provided with one transfer stage (generally four electrodes). As a method of configuring this structure, a solid state image pickup device having the structure shown in FIG. 9 has been proposed.
FIG. 9 is a schematic plan view showing at a larger scale a partial area of a solid image pickup device of the non-interlace type that signals of all pixels of one frame can be read at the same time. Reference numeral 1 represents a photoelectric conversion element (hereinafter also called a photosensor) such as a photodiode. Photosensors 1 surrounded by each broken line 2 and disposed in the vertical direction as viewed in FIG. 9 (hereinafter called a column direction) constitute a photosensor column. Photosensors 1 surrounded by each broken line 3 and disposed in the horizontal direction (hereinafter called a row direction) constitute a first photosensor row. Photosensors 1 surrounded by each broken line 4 and disposed in the horizontal direction constitute a second photosensor row. The first and second photosensor rows 3 and 4 are alternately Juxtaposed in the column direction.
Reference numeral 5 represents a first column direction charge transfer device for reading signal charges of the photosensors 1 disposed on the left side and transferring the read charges in the column direction. Reference numeral 6 represents a second column direction charge transfer device for reading signal charges of the photosensors 1 disposed on the right side and transferring the read charges in the column direction. The first and second column direction charge transfer devices 5 and 6 are disposed on both sides of each photosensor column 2.
Reference numeral 7 represents a controller for controlling to select signal charges transferred by either the first or second column direction charge transfer device 5, 6 and transferring the selected signal charges to a row direction charge transfer device 8 which transfers the received signal charges in the row direction. Reference numeral 9 represents an output circuit for generating voltages corresponding to the amounts of signal charges transferred from the row direction charge transfer device 8 and outputting the generated voltages to an external circuit (not shown). The photosensors 1, column direction charge transfer devices 5 and 6, controllers 7, row direction charge transfer device 8 and output circuit 9 are all integrally formed on a single semiconductor substrate (not shown).
In the above-described solid state image pickup device shown in FIG. 9, the column direction charge transfer devices 5 and 6 are disposed on both sides of each photosensor column 2 to provide one transfer stage 10 per one photosensor 1. Each of the column direction charge transfer devices 5 and 6 is constituted of a plurality of transfer stages 10 disposed in the column direction. The transfer stage 10 includes charge signal storage regions (packets).
Since the column direction charge transfer devices 5 and 6 are disposed in two columns between adjacent two photosensor columns 2, the distance between the photosensors 1 or photosensor columns 2 in the horizontal direction (row direction) becomes about a twofold of a distance of an interlace device structure. This area between the photosensors 2 is a photoelectrically inactive area which narrows an aperture of image sampling (photoelectrically active area) and may generate false signals such as moire.
Since the photoelectrically inactive area is broad, the area of each photosensor 1 reduces so that the amount of light incident upon the photosensor 1 reduces and hence the photoelectric conversion sensitivity lowers. A more significant problem is a difficulty of realizing high integration.
Further, the directions of reading signal charges from the photosensors 1 in the column direction change alternately right and left in the row direction (indicated by right- and left-hand arrows). If the relative position of the photosensor column 2 and the column direction charge transfer devices 5 and 6 is displaced during the manufacture processes of solid state image pickup devices, the characteristics of reading all pixel signals at the same time change between the upper and lower photosensors 1. For example, if the photosensors 1 are displaced to the right relative to the column direction charge transfer devices 5 and 6, the relative position of the photosensors 1 constituting the first photosensor row 3 and the first column transfer device 5 becomes short whereas the relative position of the photosensors 1 constituting the second photosensor row 4 and the second column transfer device 6 becomes long. Therefore, signal charges of the first photosensor row 3 are easy to read, whereas signal charges of the second photosensor row 4 are difficult to read.
Still further, since the amounts of false signals called smear are different between the first and second column direction charge transfer devices 5 and 6, a display quality is degraded because vertical stripe patterns are formed. Smear is generated by the leakage of a fraction of light incident upon the photosensor 1 to the column direction charge transfer devices 5 and 6.